1. Field
The present invention relates generally to optical metrology and, more particularly, to photolithography used in semiconductor manufacturing.
2. Description of the Related Art
Over the past thirty years the microelectronics industry has experienced dramatic rapid decreases in critical dimension by moving constantly improving photolithographic imaging systems. Today, these photolithographic systems are pushed to performance limits. As the semiconductor industry rapidly approaches limits of optical lithography, new metrology techniques will be required to measure the integrity of the photolithographic exposure machines and the devices they help produce. Specifically, metrology techniques that can accurately determine the aberrations of the projection system as well as the alignment precision of the exposure machines will be a necessity. In addition, these new metrology techniques will require advances in the methods used to guarantee the integrity of the collected data.
Conventional techniques for collecting overlay data includes programming an overlay tool with a set of software instructions that instructs the overlay tool to measure the alignment attributes (such as, bar-in-bar, box-in-box, and others) in a distinct order. The labeling and identification of the overlay output data usually depends on the type of overlay tool used to measure the alignment attributes. For example, the KLA 5200 series tools (see, for example, KLA-Tencor, “KLA 5200 Overlay Brochure”) use a complicated coding system that requires a fair degree of interpretation to decode the output data. Other tools, like the BioRad Q7 (see, for example, Bio-Rad Semiconductor Systems, “Quaestor Q7 Brochure”), simply label the output data, matching each registration error to its unique field point. However, it is important to consider that most overlay tools are programmed to measure the overlay or registration error of identical target structures that are located in close proximity of one another. Most overlay tools use an optical recognition routine to identify each alignment attribute before each measurement. Oftentimes the optical recognition system can read the wrong alignment attribute or a similar looking feature in a systematic way. If one simply assumes that the overlay tool has identified the correct alignment attribute and proceeds to use the program for production measurements, the data can become corrupt. In addition, many times the alignment attributes and wafer exposure patterns are symmetric with respect to the notch of the wafer, and simple rotations of the wafer can cause a good deal of confusion when trying to verify the results visually. Therefore, in some cases, even if the output data is labeled correctly there is really no way to independently verify the integrity of the results for common machine and overlay tool programming errors.
Recently, extrinsic, or non-embedded, techniques for verifying overlay data orientation have been developed (see, for example, McArthur et al., “Method and Apparatus for Proper Ordering of Registration Data”, U.S. Pat. No. 6,833,221, Dec. 21, 2004). While these extrinsic techniques are useful they require that the user actually perform additional exposures and measurements. These additional exposures and measurements can be troublesome for semiconductor manufacturing facilities that limit excess metrology.
Thus, a need exists for improved methods and apparatus that can independently verify the integrity of an overlay set-up program and output data results before using the job deck programs for production applications. It is also desirable to minimize data collection during verification of the overlay set-up program.